The purpose of this program are to complete the development of electrically powered, totally implantable artificial heart (TAH) systems and establish the reliability, performance and manufacturability of these TAH systems as a prerequisite to consideration for an NHLBI Clinical Trial. Phase I (3 years; up to four contracts) comprises design completion, demonstration of manufacturability, performance testing in animals and demonstration of the contractor's capability to begin Phase II device readiness testing. Phase II (4 years; less than four contracts) will provide support for those contractors who successfully complete Phase I and are judged meritorious by peer-review. Phase II consists of in vitro reliability and in vivo animal testing of tether-free implantable total artificial heart systems.